Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$53.62	10.733%	$59.375	$59.38	$59.40	$59.40
Purchase #2	$194.68	10.125%	$214.3914	$214.39	$214.40	$214.40
Purchase #3	$28.58	10.172%	$31.4872	$31.49	$31.50	$31.50
Purchase #4	$217.45	9.720%	$238.5861	$238.59	$238.60	$238.60
Purchase #5	$60.81	12.128%	$68.185	$68.19	$68.20	$68.20
Purchase #6	$75.55	8.738%	$82.1516	$82.15	$82.15	$82.20
Purchase #7	$111.49	10.835%	$123.5699	$123.57	$123.55	$123.60
7 purchase totals =	$742.18		$817.7462	$817.76	$817.80	$817.90